Method and apparatus for providing uplink signal-to-noise ratio (SNR) estimation in a wireless communication

ABSTRACT

A method and apparatus for providing uplink signal-to-noise ratio (SNR) estimation in a wireless communication system. A first signal is received over a first channel and a second signal is received over a second channel, where the second signal is received at a higher signal power level than said first signal. A signal-to-noise ratio (SNR) of the second signal is measured, and the SNR of the first signal is determined based at least in part upon the measured SNR of the second signal.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

This application claims priority to U.S. Provisional Application No.60/452,790 filed Mar. 6, 2003, entitled “Method and Apparatus for aReverse Link Communication in a Communication System,” and assigned tothe assignee hereof and hereby expressly incorporated by referenceherein.

BACKGROUND

1. Field

The present invention relates generally to communication systems, and,more specifically, to a method and apparatus for providing uplinksignal-to-noise ratio (SNR) estimation in a wireless communicationsystem.

2. Background

Wireless communication technologies have seen explosive growth over thepast few years. This growth has been primarily fueled by wirelessservices providing freedom of movement to the communicating public asopposed to being “tethered” to a hard-wired communication system. It hasalso been fueled by the increasing quality and speed of voice and datacommunications over the wireless medium, among other factors. As aresult of these enhancements in the communications field, wirelesscommunications has had, and will continue to have, a significant impacton a growing number of the communicating public.

One type of wireless communication system includes a Wideband CodeDivision Multiple Access (W-CDMA) system, which is configured to supportboth voice and data communications. This system may have multiple basetransceiver sites that communicate over a wireless link with a pluralityof mobile terminals. The base transceiver site transmits data andcontrol information to the mobile terminal over a set of forward linkchannels and the mobile terminal transmits data and control informationto the base transceiver site over a set of reverse link channels. Inparticular, the reverse link channels transmitted from the mobileterminal to the base transceiver site include a pilot channel, trafficchannel, and rate indicator channel, among others. The traffic channeltransmits data from the mobile terminal to the base transceiver site.The rate indicator channel provides a data rate to the base transceiversite indicating the rate at which data is being transmitted over thetraffic channel. The pilot channel may be used by the base transceiversite for an amplitude and phase reference for demodulating the data onthe traffic channel.

The reverse link channels are typically power controlled to compensatefor variations in the received signals due to variations through thecommunication medium between the mobile terminal and base transceiversite. This power control process is usually based on measuring thesignal-to-noise ratio (SNR) of the pilot channel. For example, the basetransceiver site periodically measures the SNR of the pilot channelreceived from the mobile terminal and compares it to a target SNR. Ifthe measured SNR is below the target SNR, the base transceiver sitetransmits to the mobile terminal an “UP” command. This directs themobile terminal to increase the power level of the pilot channel, aswell as the other channels. If the measured SNR is above the target SNR,the base transceiver site sends a “DOWN” command to the mobile terminal.This directs the mobile terminal to decrease the power level of thechannels. The mobile terminal increases or decreases the transmit powerof the channels by a fixed upward or downward step.

Typically, as the data rate on the traffic channel increases, the signalpower of the traffic channel is also increased by the mobile terminal toaccommodate the increased data rate. For an efficient operation of thecommunication link, the pilot power typically needs to be increased toprovide better phase estimation for the higher data rates. However,because the maximum total signal power at which the mobile terminal maytransmit over each of the reverse link channels is limited to a finiteamount of power, the signal power level of the pilot channel is set to anominal signal power level to enable an increase in the signal powerlevel of the traffic channel to accommodate the increased data rate andminimize the pilot channel overhead. By keeping the signal power levelof the pilot channel to a nominal signal power level, the estimation ofthe SNR of the pilot channel may not be as precise as if it weretransmitted at a higher signal power level. As a result, the inner-looppower control of the wireless communication system may be adverselyimpacted due to the decreased reliability in the measured SNR of a lowersignal power level transmitted on the pilot channel.

The present invention is directed to overcoming, or at least reducingthe effects of, one or more problems indicated above.

SUMMARY

In one aspect of the invention, a method in a wireless communicationsystem is provided. The method comprises receiving a first signal over afirst channel and a second signal over a second channel, where thesecond signal is received at a higher signal power level than the firstsignal. A signal-to-noise ratio (SNR) of the second signal is measured,and the SNR of the first signal is determined based at least in partupon the measured SNR of the second signal.

In another aspect of the invention, an apparatus is provided. Theapparatus comprises at least one transmitter for transmitting a firstsignal over a first channel and a second signal over a second channel,where the second signal is transmitted at a higher signal power levelthan the first signal. The system further comprises at least onereceiver for receiving the first and second signals. The receivermeasures a signal-to-noise ratio (SNR) of the second signal anddetermines the SNR of the first signal based at least in part upon themeasured SNR of the second signal.

In another aspect of the invention, a device is provided. The devicecomprises a receiver for receiving a first signal over a first channeland a second signal over a second channel, where the second signal isreceived at a higher signal power level than the first signal. Thereceiver device further comprises a processor for measuring asignal-to-noise ratio (SNR) of the second signal and determining the SNRof the first signal based at least in part upon the measured SNR of thesecond signal.

In another aspect of the invention, a mobile terminal is provided. Themobile terminal comprises a transmitter that transmits a first signalover a first channel and a second signal over a second channel to a basetransceiver site, where the second signal is transmitted at a highersignal power level than the first signal. The base transceiver sitereceives the first and second signals, measures a signal-to-noise ratio(SNR) of the second signal, and determines the SNR of the first signalbased at least in part upon the measured SNR of the second signal.

In another aspect of the invention, a computer readable media embodyinga method for a wireless communication system is provided. The methodcomprises receiving a first signal over a first channel and a secondsignal over a second channel, where the second signal is received at ahigher signal power level than the first signal. A signal-to-noise ratio(SNR) of the second signal is measured, and the SNR of the first signalis determined based at least in part upon the measured SNR of the secondsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless communication system inaccordance with one illustrative embodiment of the present invention;

FIG. 2 shows a more detailed representation of a mobile terminal thatcommunicates in the wireless communication system of FIG. 1;

FIG. 3 depicts a more detailed representation of a base transceiver sitewithin the wireless communication system of FIG. 1;

FIG. 4 is a diagram illustrating forward and reverse link channels usedbetween the mobile terminal and the base transceiver site;

FIGS. 5A and 5B show the transmission of a rate indicator channel in acode division multiplex (CDM) and time division multiplex (TDM) manner,respectively;

FIG. 6 illustrates a plot conveying the relative signal power levels atwhich a traffic channel, rate indicator channel, and pilot channel aretransmitted by the mobile terminal to the base transceiver site;

FIG. 7 shows a look-up table, which is stored at the base transceiversite, that provides a relationship between a data rate of the trafficchannel, a traffic-to-pilot ratio, and a RICH-to-pilot ratio of therespective reverse link channels; and

FIG. 8 is a flow diagram illustrating a method for providing anestimation of a pilot SNR and symbol SNR in accordance with oneembodiment of the present invention.

DETAILED DESCRIPTION

Turning now to the drawings, and specifically referring to FIG. 1, awireless communication system 100 is shown in accordance with oneembodiment of the present invention. The wireless communication system100 comprises a plurality of mobile terminals (MT) 105 that communicatewith a plurality of base transceiver sites (BTS) 110, which aregeographically dispersed to provide continuous communication coveragewith the mobile terminals 105 as they traverse the wirelesscommunication system 100.

The mobile terminals 105 may, for example, take the form of wirelesstelephones, personal information managers (PIMs), personal digitalassistants (PDAs), or other types of computer terminals that areconfigured for wireless communication. The base transceiver sites 110transmit data to the mobile terminals 105 over a forward link of awireless communication channel 115, and the mobile terminals 105transmit data to the base transceiver sites 110 over a reverse link ofthe channel 115.

In one embodiment, the wireless communication system 100 conformsgenerally to a release of the W-CDMA (Wideband Code Division MultipleAccess) specification. W-CDMA is a 3rd Generation (3G) wirelesscommunication standard that is based on the IS-95 standard. Inaccordance with the illustrated embodiment, the wireless communicationsystem 100 is intended to operate utilizing 3GPP (3^(rd) GenerationPartnership Project) Release 6 of the W-CDMA standard, but otherembodiments may be implemented in other releases of the W-CDMA standard.In an alternative embodiment, the wireless communication system 100 mayoperate in accordance with 3GPP2 Revision D of the cdma2000 standard. Itwill be appreciated that the embodiments described herein should beconsidered as exemplary rather than limiting. Accordingly, the system100 may take the form of various other types of wireless communicationsystems without departing from the spirit and scope of the presentinvention.

Each base-transceiver site 110 is coupled to a base station controller(BSC) 120, which controls connections between the base transceiver sites110 and other communication system components of the wirelesscommunication system 100. The base transceiver sites 110 and the basestation controller 120 collectively form a radio access network (RAN)for transporting data to and from the plurality of mobile terminals 105that communicate within the wireless communication system 100. The basetransceiver sites 110 are coupled to the base station controller 120 bycommunication links 125, which may take the form of a wireline E1 or T1link. The communication links 125, however, may alternatively beembodied using any one of a number of wired or wireless communicationmediums including, but not necessarily limited to, microwave, opticalfiber, and the like. Additionally, the simplified depiction of thewireless communication system 100 in FIG. 1 is merely for ease inconveying the present invention. It will be appreciated, however, thatthe wireless communication system 100 may be configured with any numberof mobile terminals 105, base transceiver sites 110, and base stationcontrollers 120 without departing from the spirit and scope of thepresent invention.

The base station controller 120 may be coupled to various communicationsystem components to effectively extend the communication capabilitiesavailable to the mobile terminals 105 beyond the wireless communicationsystem 100. The communication system components may include a dataserver 140, a public switched telephone network (PSTN) 150, and theInternet 160 for access by the mobile terminals 105. It will beappreciated that the communication system components illustrated in FIG.1 are for exemplary purposes only, and that the wireless communicationsystem 100 may be interfaced with various other types of communicationsystem components without departing from the spirit and scope of thepresent invention.

Turning now to FIG. 2, a more detailed representation of the mobileterminal 105 is shown in accordance with one embodiment of the presentinvention. In one of its simpler forms, the mobile terminal 105comprises a transmitter 205 for transmitting data over the reverse linkof the wireless communication channel 115 to the base transceiver sites110. The mobile terminal 105 also includes a receiver 210 for receivingdata transmitted from the base transceiver sites 110 over the forwardlink of the wireless communication channel 115. In an alternativeembodiment, the transmitter 205 and receiver 210 may be combined into asingle transceiver unit as opposed to being embodied as two separateentities as illustrated in the figure. The transmitter 205 and thereceiver 210 are coupled to an antenna 215 to facilitate the wirelesstransmission and reception of data over the wireless communicationchannel 115.

The mobile terminal 105 further comprises a processor 220 forcontrolling various operating functions and a memory 225 for storingdata. In one embodiment, the processor 220 may take the form of adigital signal processor (DSP) chip. It will be appreciated, however,that the processor 220 may take the form of various othercommercially-available processors or controllers.

The mobile terminal 105 also comprises a data input unit 230, whichprovides data for transmission to the base transceiver sites 110 overthe wireless communication channel 115. The data input unit 230 may takethe form of a microphone or an input from a data generating device, suchas a computer terminal, for example. It will be appreciated that thedata input unit 230 may be implemented in various other forms to providedata to the processor 220, and, thus, need not necessarily be limited tothe aforementioned examples.

The data received through the data input unit 230 is processed by theprocessor 220 and then forwarded to the transmitter 205 for transmissionover the reverse link of the wireless communication channel 115 to thebase transceiver sites 110. Data received by the receiver 210 over theforward link of the wireless communication channel 115 from the basetransceiver sites 110 is forwarded to the processor 220 for processingand then to data output unit 235 for various purposes, such aspresentation to the user of the mobile terminal 105, for example. Thedata output unit 235 may take the form of at least one of a speaker,visual display, and an output to a data device (e.g., a computerterminal), or any combination thereof. It will be appreciated that thedata output unit 235 may comprise various other visual or auralperceptible devices, and, thus, need not necessarily be limited to theaforementioned examples. Furthermore, the simplified depiction of themobile terminal 105 in FIG. 2 is merely for ease in conveying thepresent invention. Accordingly, it will also be appreciated that themobile terminal 105 may include other components to enable various otherfeatures and/or capabilities of the mobile terminal 105 than thoseillustrated.

Referring now to FIG. 3, a more detailed representation of the basetransceiver site 110 is shown according to one embodiment of the presentinvention. In one of its simpler forms, the base transceiver site 110comprises a transmitter 305 for transmitting data over the forward linkof the wireless communication channel 115 to the mobile terminal 105,and a receiver 310 for receiving data from the mobile terminals 105 overthe reverse link of the wireless communication channel 115. In analternative embodiment, the transmitter 305 and receiver 310 may becombined into a single transceiver unit as opposed to being embodied astwo separate entities as illustrated. The transmitter 305 and thereceiver 310 are coupled to an antenna 315 to facilitate thetransmission and reception of data over the wireless communicationchannel 115.

The base transceiver site 110 is further configured with a processor 320for controlling various operating features and a memory 325 for storingdata. In one embodiment, the processor 320 may take the form of adigital signal processor (DSP) chip. It will be appreciated, however,that the processor 320 may take the form of various othercommercially-available processors or controllers. The base transceiversite 110 further comprises a communication interface 340 for interfacingthe base transceiver site 110 to the base station controller 120. Itwill be appreciated that the base transceiver site 110 may be configuredwith additional components to perform a variety of other functions thanthose illustrated.

The wireless communication channel 115 includes various channels forcommunication between the base transceiver site 110 and the mobileterminal 105. Referring to FIG. 4, a diagram illustrating the pluralityof channels between the base transceiver site 110 and the mobileterminal 105 is shown. Base transceiver site 110 transmits data tomobile terminal 105 via a set of forward link channels 410. Theseforward link channels 410 typically include data channels through whichdata is transmitted and control channels through which control signalsare transmitted.

Mobile terminal 105 transmits data to the base transceiver site 110 viaa set of reverse link channels 420, which also include both data andcontrol channels. In particular, the mobile terminal 105 transmitsinformation to the base transceiver site 110 over a dedicated physicalcontrol channel (DPCCH) (e.g., a pilot channel) 422, a dedicatedphysical data channel (R-DPDCH) (e.g., a traffic channel) 424, and arate indicator channel (R-RICH) 426.

The information transmitted over these reverse link channels 420 fromthe mobile terminal 105 to the base transceiver site 110 is representedby bits. Several bits are grouped together into a frame and encoded intomodulation symbols. The modulation symbols are then transmitted over theappropriate reverse link channels 420 to the base transceiver site 110.For example, rate indicator bits are encoded into rate indicatormodulation symbols and are then transmitted over the rate indicatorchannel R-RICH 426. Similarly, bits of traffic data are encoded intodata modulation symbols, and transmitted over the traffic channelR-DPDCH 424.

The traffic channel R-DPDCH 424 carries a signal comprising frames ofdata from the mobile terminal 105 to the base transceiver site 110. Thedata rate at which these frames are transmitted is typically variable.Usually, as the data rate over the traffic channel R-DPDCH 424increases, the amount of power needed to transmit the data trafficsignal over the traffic channel R-DPDCH 424 also increases.

The rate indicator channel R-RICH 426 carries a signal comprising rateindicator frames that correspond to the data traffic frames transmittedon the traffic channel R-DPDCH 424. Each of the rate indicator framesidentifies the data rate of the corresponding data traffic frame. Therate indicator channel R-RICH 426 further carries Hybrid AutomaticRepeat Request (HARQ) information (such as sub-packet ID, redundancyversion, etc.), which enables the base transceiver site 110 to decodethe traffic channel R-DPDCH 424. The HARQ bits enable the basetransceiver site 110 to either soft-combine the received data symbolswith previous transmissions over the traffic channel R-DPDCH 424 priorto decoding or to decode the received symbols independently. The rateindicator channel R-RICH 426 typically has a fixed, low data rate.

The pilot channel DPCCH 422 carries a pilot signal that provides anamplitude and phase reference, for example, for demodulating the data onthe traffic channel R-DPDCH 424. Accordingly, the pilot channel DPCCH422 may be used as a demodulation reference by the base transceiver site110 for demodulating received signals from the mobile terminal 105. Inaccordance with the illustrated embodiment, the pilot signal has afixed, low data rate to enable the mobile terminal 105 to transmit overthe traffic channel R-DPDCH 424 at a higher signal power to accommodatehigher data rates transmitted thereover.

In one embodiment, the rate indicator channel R-RICH 426 is transmittedin a code division multiplex (CDM) manner as illustrated in FIG. 5A, inwhich the rate indicator channel R-RICH 426 is transmitted on a separatecode channel from the traffic channel R-DPDCH 424. In an alternativeembodiment, the rate indicator channel R-RICH 426 may be transmitted ina time division multiplex (TDM) manner with the traffic channel R-DPDCH424 on the same code channel on a time division basis as illustrated inFIG. 5B.

Typically, as the data rate on the traffic channel R-DPDCH 424increases, the signal power of the traffic channel R-DPDCH 424 is alsoincreased by the mobile terminal 105 to accommodate the increased datarate. For an efficient operation of the communication link, the pilotpower is typically increased to provide better phase estimation forhigher data rates. Because the maximum total signal power at which themobile terminal 105 may transmit over each of the reverse link channels420 is limited to a finite amount of power, the signal power level ofthe pilot channel DPCCH 422 is set to a nominal signal power level toenable an increase in the signal power level of the traffic channelR-DPDCH 424 to accommodate the increased data rate and minimize thepilot channel DPCCH 422 overhead.

By keeping the signal power level of the pilot channel DPCCH 422 to anominal signal power level, however, the estimation of thesignal-to-noise ratio (SNR) of the pilot channel DPCCH 422 may not be asprecise as if it were transmitted at a higher signal power level. Bymeasuring the SNR of the rate indicator channel R-RICH 426, which istransmitted at a higher signal power level than the pilot channel DPCCH422, a more accurate estimation of the pilot channel SNR may bedetermined. As a result of achieving a more accurate SNR of the pilotchannel DPCCH 422, the wireless communication system 100 may achieve amore efficient inner-loop power control and symbol scaling for turbodecoding.

Turning now to FIG. 6, a plot illustrating the relative signal powerlevels at which the traffic channel R-DPDCH 424, rate indicator channelR-RICH 426, and pilot channel DPCCH 422 are transmitted by the mobileterminal 105 to the base transceiver site 110 is shown for a particulardata rate. In accordance with the illustrated embodiment, the signalpower level of the pilot channel DPCCH 422 is kept to a nominal level topermit the traffic channel R-DPDCH 424 to be transmitted at a highersignal power level to accommodate a higher data rate. In the illustratedembodiment, the traffic-to-pilot (T/P) ratio (i.e., the energy-per-chipratio of the data signal on the traffic channel R-DPDCH 424 to the pilotsignal on the pilot channel DPCCH 422) is kept relatively high ascompared to the RICH-to-pilot (R/P) ratio (i.e., the energy-per-chipratio of the rate indicator signal on the rate indicator channel R-RICH426 to the pilot signal on the pilot channel DPCCH 422). As the datarate increases over the traffic channel R-DPDCH 424, the differencebetween the traffic-to-pilot and RICH-to-pilot ratios also increases.The relationship between the traffic-to-pilot and RICH-to-pilot ratiosplays a significant role in determining the SNR of the pilot channelDPCCH 422 and the traffic channel R-DPDCH 424.

Referring now to FIG. 7, a look-up table 700 providing a relationshipbetween a data rate 710 of the traffic channel R-DPDCH 424 and a desiredtraffic-to-pilot ratio 720 and RICH-to-pilot ratio 730 is shownaccording to one embodiment of the present invention. In accordance withone embodiment, the table 700 is stored within the memory 325 of thebase transceiver site 110, and provides the desired traffic-to-pilotratio 720 and RICH-to-pilot ratio 730 for each particular data rate 710at which the mobile terminal 105 transmits data over the traffic channelR-DPDCH 424 to the base transceiver site 110. As the data rate 710 ofthe traffic channel R-DPDCH 424 increases, the difference between thetraffic-to-pilot ratio 720 and the RICH-to-pilot ratio 730 increases. Itwill be appreciated that the specific values of the traffic-to-pilot andRICH-to-pilot ratios 720, 730 for the particular data rates 710 providedwithin the table 700 are merely exemplary. Accordingly, the values ofthe traffic-to-pilot and RICH-to-pilot ratios 720, 730 need notnecessarily be limited to the examples shown, but may include othervalues without departing from the spirit and scope of the presentinvention.

The RICH-to-pilot ratio 730 within the table 700 for a particular datarate 710 is used by the base transceiver site 110 to more accuratelyestimate the SNR of the pilot channel DPCCH 422 and the traffic channelR-DPDCH 424. Specifically, in one embodiment, the estimated SNR of thepilot channel DPCCH 422 is the product of the measured SNR of the rateindicator channel R-RICH 426 and the inverse of the RICH-to-pilot ratio730 for a particular data rate 710 over the traffic channel R-DPDCH 424.The symbol SNR for the traffic channel R-DPDCH 424 is the product of themeasured SNR of the rate indicator channel R-RICH 426, the inverse ofthe RICH-to-pilot ratio 730, and the traffic-to-pilot ratio 720 for aparticular data rate 710 over the traffic channel R-DPDCH 424. Theestimated pilot SNR is used by the base transceiver site 110 to moreaccurately perform inner-loop power control and the estimated symbol SNRis used for metric scaling in turbo decoding. A more detaileddescription of how the base transceiver site 110 determines the pilotSNR and symbol SNR is provided below.

To determine the SNR of the pilot channel DPCCH 422, the SNR of the rateindicator channel R-RICH 426 is measured. According to the illustratedembodiment, symbols from the traffic channel R-DPDCH 424 are stored inthe memory 325 of the base transmitter site 110 as they are receivedfrom the mobile terminal 105. The normalized RICH symbol (x_(k)) fromthe rate indicator channel R-RICH 426 that is received after pilotfiltering (e.g., channel estimation and de-rotation) may be representedby the following equation.

$\begin{matrix}{x_{k} = {{{\alpha_{k}}^{2} \cdot \sqrt{\frac{E_{cp}}{I_{o}}} \cdot \sqrt{\frac{E_{c,{rich}} \cdot {SF}}{I_{o}}} \cdot {\mathbb{e}}^{j \cdot \phi}} + {\alpha^{*} \cdot \sqrt{\frac{E_{cp}}{I_{o}}} \cdot \sqrt{\frac{N_{t}}{2 \cdot I_{o}}} \cdot}}} \\{\left\{ {n_{kl} + {j \cdot n_{kQ}}} \right\}} \\{p_{k} = {{\alpha \cdot \sqrt{\frac{E_{cp} \cdot {SF}_{p}}{I_{o}}} \cdot {\mathbb{e}}^{j \cdot \phi}} + {\sqrt{\frac{N_{t}}{2 \cdot I_{o}}} \cdot \left\{ {u_{kl} + {j \cdot u_{kQ}}} \right\}}}}\end{matrix}$wherein α_(k)=Fading coefficient

-   -   E_(c,rich)=Energy per RICH chip    -   E_(cp)=Energy per Pilot chip    -   SF=Spread Factor of RICH    -   SF_(p)=Spread Factor of Pilot    -   I_(o)=Total Received power spectral density    -   φ=Phase    -   N_(t)=Noise plus Interference power spectral density        n_(k1), n_(kQ), u_(k1), u_(kQ)=Complex noise plus interference        terms

The SNR of the rate indicator channel R-RICH 426 may be determined byeither accumulating the RICH symbols non-coherently, coherently, or acombination of coherent and non-coherent accumulation. When accumulatingthe RICH symbols non-coherently, each RICH symbol's energy is summedacross the RICH transmission. An example of non-coherent accumulationmay be represented by the following equation, which provides an estimateof the RICH symbol energy (E_(s,rich)/I_(o)).

$\frac{E_{s,{rich}}}{I_{o}} = {\frac{1}{N} \cdot {\sum\limits_{k = 0}^{N - 1}\;{x_{k}}^{2}}}$An estimate of the noise power spectral density (N_(t)/I_(o)) isrepresented by the following equation.

$\frac{N_{t}}{I_{o}} = {\frac{1}{N - 1} \cdot {\sum\limits_{k = 0}^{N - 2}\;{{p_{k + 1} - p_{k}}}^{2}}}$

When accumulating the RICH symbols coherently, the base transceiver site110 decodes the RICH first. If the RICH symbols are repeated across thetransmission, the RICH may be decoded after each transmission. Once thedecoding is successfully completed, the base transceiver site 110 knowsthe transmitted RICH symbols and may then coherently sum the receivedsymbols. An example of coherent accumulation may be represented by thefollowing equation, which provides an estimate of the RICH symbol energy(E_(s,rich)/I_(o))

$\frac{E_{s,{rich}}}{I_{o}} = {y}^{2}$where:

$y = {\frac{1}{N} \cdot {\sum\limits_{k = 0}^{N - 1}\;{x_{k} \cdot z_{k}}}}$z_(k)=Estimated RICH symbol at time k

An estimate of the noise power spectral density (N_(t)/I_(o)) may berepresented by the following equation.

$\frac{N_{t}}{I_{o}} = {\frac{1}{N - 1} \cdot {\sum\limits_{k = 0}^{N - 2}\;{{{z_{k + 1} \cdot x_{k + 1}} - {z_{k} \cdot x_{k}}}}^{2}}}$For non-coherent and coherent accumulations, the SNR (E_(s,rich)/N_(t))of the rate indicator channel R-RICH 426 may then be derived by thefollowing equation.

$\frac{E_{s,{rich}}}{N_{t}} = {\frac{E_{s,{rich}}}{I_{o}} \cdot \frac{I_{o}}{N_{t}}}$

Once the SNR (E_(s,rich)/N_(t)) of the rate indicator channel R-RICH 426is obtained, the SNR (E_(c,pilot)/N_(t)) of the pilot channel DPCCH 422may be obtained from the equation below.

$\frac{E_{c,{pilot}}}{N_{t}} = {\frac{E_{s,{rich}}}{N_{t}} \cdot \frac{E_{c,{pilot}}}{E_{c,{rich}}}}$In particular, the SNR (E_(c,pilot)/N_(t)) of the pilot channel DPCCH422 is determined by taking the product of the measured SNR(E_(s,rich)/N_(t)) of the rate indicator channel R-RICH 426 (as obtainedabove) and the inverse of the RICH-to-pilot ratio 730 for a particulardata rate over the traffic channel R-DPDCH 424 from the table 700 storedwithin memory 325 of the base transceiver site 110. As mentioned, theRICH-to-pilot ratio 730 is the energy-per-chip ratio between the rateindicator signal and the pilot signal (E_(c,rich)/E_(c,pilot)). Once theSNR (E_(c,pilot)/N_(t)) of the pilot channel DPCCH 422 is obtained, thepilot SNR may be used to more accurately perform inner-loop powercontrol by the base transceiver site 110 for communicating with themobile terminal 105. The manner in which the base transceiver site 110performs inner-loop power control based on an estimated pilot SNR iswell known to those of ordinary skill in the art. Accordingly, thedetails for determining such power control based on the pilot SNR willnot be disclosed herein to avoid unnecessarily obscuring the presentinvention.

The symbol SNR (E_(s,data)/N_(t)) for metric scaling may be derived bythe following equation.

$\frac{E_{s,{data}}}{N_{t}} = {\frac{E_{s,{rich}}}{N_{t}} \cdot \frac{E_{c,{data}}}{E_{c,{pilot}}} \cdot \frac{E_{c,{pilot}}}{E_{c,{rich}}}}$The symbol SNR (E_(s,data)/N_(t)) is determined by taking the product ofthe measured SNR (E_(s,rich)/N_(t)) of the rate indicator channel R-RICH426, the inverse of the RICH-to-pilot ratio 730, and thetraffic-to-pilot ratio 720 for a particular data rate over the trafficchannel R-DPDCH 424. As previously mentioned, the RICH-to-pilot ratio730 and traffic-to-pilot ratio 720 for a particular data rate 710 on thetraffic channel R-DPDCH 424 are obtained from the table 700 storedwithin the memory 325 of the base transceiver site 110. The estimatedsymbol SNR (E_(s,data)/N_(t)) is then used by the base transceiver site110 for metric scaling in turbo decoding. The manner in which the basetransceiver site 110 performs metric scaling based on an estimatedsymbol SNR is well known to those of ordinary skill in the art.Accordingly, the details for determining such metric scaling based onthe symbol SNR will not be disclosed herein to avoid unnecessarilyobscuring the present invention.

Turning now to FIG. 8, a method for providing an estimation of a pilotSNR and symbol SNR is shown in accordance with one embodiment of thepresent invention. At block 810, the receiver 310 of the basetransceiver site 110 receives the pilot, data, and rate indicatorsignals over the respective pilot channel DPCCH 422, traffic channelR-DPDCH 424, and rate indicator channel R-RICH 426 transmitted from themobile terminal 105. According to one embodiment, the rate indicatorchannel R-RICH 426 is transmitted in a code division multiplex (CDM)manner as illustrated in FIG. 5A, in which the rate indicator channelR-RICH 426 is transmitted on a separate code channel from the trafficchannel R-DPDCH 424. In an alternative embodiment, the rate indicatorchannel R-RICH 426 may be transmitted in a time division multiplex (TDM)manner with the traffic channel R-DPDCH 424 on the same code channel ona time division basis as illustrated in FIG. 5B.

At block 820, the base transceiver site 110 stores symbols from thetraffic channel R-DPDCH 424 as they are received from the mobileterminal 105. The processor 320 of the base transceiver site 110estimates the SNR of the rate indicator channel R-RICH 426 eithernon-coherently, coherently, or a combination of both coherent andnon-coherent accumulation at block 830. Specifically, when accumulatingthe RICH symbols non-coherently, each RICH symbol's energy is summedacross the RICH transmission. When accumulating the RICH symbolscoherently, the base transceiver site 110 decodes the RICH first. If theRICH symbols are repeated across the transmission, the RICH may bedecoded after each transmission. Once the decoding is successfullycompleted, the base transceiver site 110 knows the transmitted RICHsymbols and may then coherently sum the received symbols. Examples ofnon-coherent and coherent accumulation, which provide an estimate of theRICH symbol energy (E_(s,rich)/I_(o)) have been previously provided. Inone embodiment, the SNR (E_(s,rich)/N_(t)) of the rate indicator channelR-RICH 426 may then be derived by taking the product of the RICH symbolenergy (E_(s,rich)/I_(o)) and the inverse of the noise power spectraldensity (N_(t)/I_(o)), the equations of which have been also previouslyprovided.

At block 840, the processor 320 of the base transceiver site 110determines the pilot SNR (E_(c,pilot)/N_(t)) of the pilot channel DPCCH422 by taking the product of the measured SNR of the rate indicatorchannel R-RICH 426 and the inverse of the RICH-to-pilot ratio 730 for aparticular data rate 710 over the traffic channel R-DPDCH 424 from thetable 700 stored within memory 325 of the base transceiver site 110 asshown by the equation below.

$\frac{E_{c,{pilot}}}{N_{t}} = {\frac{E_{s,{rich}}}{N_{t}} \cdot \frac{E_{c,{pilot}}}{E_{c,{rich}}}}$Once the SNR of the pilot channel DPCCH 422 is obtained, the pilot SNRmay be used to perform inner-loop power control by the base transceiversite 110 for communicating with the mobile terminal 105 using methodswell-established in the art.

At block 850, the processor 320 of the base transceiver site 110determines the symbol SNR (E_(s,data)/N_(t)) of the traffic channelR-DPDCH 424 by taking the product of the measured SNR of the rateindicator channel R-RICH 426, the inverse of the RICH-to-pilot ratio730, and the traffic-to-pilot ratio 720 for a particular data rate overthe traffic channel R-DPDCH 424 as shown by the equation below.

$\frac{E_{s,{data}}}{N_{t}} = {\frac{E_{s,{rich}}}{N_{t}} \cdot \frac{E_{c,{data}}}{E_{c,{pilot}}} \cdot \frac{E_{c,{pilot}}}{E_{c,{rich}}}}$As previously mentioned, the RICH-to-pilot ratio 730 andtraffic-to-pilot ratio 720 for a particular data rate 710 on the trafficchannel R-DPDCH 424 are obtained from the table 700 stored within thememory 325 of the base transceiver site 110. The estimated symbol SNRmay then be used by the base transceiver site 110 for metric scaling inturbo decoding using methods well established in the art.

By keeping the signal power level of the pilot channel DPCCH 422 to anominal signal power level to accommodate higher data rates over thetraffic channel R-DPDCH 424 may cause the estimation of the SNR of thepilot channel DPCCH 422 to not be as precise as if it were transmittedat a higher signal power level. By measuring the SNR of the rateindicator channel R-RICH 426, which is transmitted at a higher signalpower level than the pilot channel R-DPCCH 422, a more accurateestimation of the pilot channel SNR may be determined using the methodsdescribed above. As a result of achieving a more accurate SNR of thepilot channel DPCCH 422, the wireless communication system 100 mayachieve a more efficient inner-loop power control and symbol scaling forturbo decoding.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method for a wireless communication system, comprising: receiving afirst signal over a first channel and a second signal over a secondchannel, said second signal being received at a higher signal powerlevel than said first signal; measuring a signal-to-noise ratio (SNR) ofthe second signal; and determining the SNR of the first signal based atleast in part upon the measured SNR of the second signal.
 2. The methodof claim 1, wherein said receiving at least a first signal over a firstchannel and a second signal over a second channel further comprises:receiving at least a pilot signal over the first channel and a rateindicator signal over the second channel, said rate indicator signalindicating a data rate at which a data signal is received over a thirdchannel.
 3. The method of claim 2, wherein said data signal is receivedover the third channel at a higher signal power level than said rateindicator signal and said pilot signal.
 4. The method of claim 2,further comprising: determining a first energy-per-chip ratio betweenthe rate indicator and pilot signals based at least in part upon saiddata rate at which said data signal is received over said third channel.5. The method of claim 4, wherein said determining the SNR of the firstsignal further comprises: determining the SNR of the pilot signal basedon the measured SNR of the rate indicator signal and the firstenergy-per-chip ratio between the rate indicator and pilot signals. 6.The method of claim 4, further comprising: determining a secondenergy-per-chip ratio between the data and pilot signals based at leastin part upon said data rate at which said data signal is received overthe third channel.
 7. The method of claim 6, further comprising:determining the SNR of the data signal based at least upon the measuredSNR of the rate indicator signal and the first and secondenergy-per-chip ratios.
 8. An apparatus, comprising: at least onetransmitter for transmitting a first signal over a first channel and asecond signal over a second channel, said second signal beingtransmitted at a higher signal power level than said first signal; andat least one receiver for receiving the first and second signals; andwherein said receiver measures a signal-to-noise ratio (SNR) of thesecond signal and determines the SNR of the first signal based at leastin part upon the measured SNR of the second signal.
 9. The apparatus ofclaim 8, wherein said first signal is a pilot signal and said secondsignal is a rate indicator signal; and wherein said raze indicatorsignal indicates a data rate at which a data signal is received from thetransmitter Over a third channel.
 10. The apparatus of claim 9, whereinsaid data signal is received over the third channel at a higher signalpower level than said rate indicator signal and said pilot signal. 11.The apparatus of claim 9, wherein said receiver determines a firstenergy-per-chip ratio between the rate indicator and pilot signals basedat least in part upon said data rate at which said data signal isreceived over said third channel.
 12. The apparatus of claim 11, whereinsaid receiver determines the SNR of the pilot signal based on themeasured SNR of the rate indicator signal and the first energy-per-chipratio between the rate indicator and pilot signals.
 13. The apparatus ofclaim 11, wherein said receiver determines a second energy-per-chipratio between the data and pilot signals based at least in part uponsaid data rate at which said data signal is received over the thirdchannel.
 14. The apparatus of claim 13, wherein said receiver determinesthe SNR of the data signal based at least upon the measured SNR of therate indicator signal and the first and second energy-per-chip ratios.15. The apparatus of claim 8, wherein said transmitter is a mobileterminal and said receiver is a base transceiver site.
 16. The apparatusof claim 8, wherein said transmitter and said receiver communicate via acode division multiple access (CDMA) scheme.
 17. A device, comprising: areceiver for receiving a first signal over a first channel and a secondsignal over a second channel, said second signal being received at ahigher signal power level than said first signal; and a processor formeasuring a signal-to-noise ratio (SNR) of the second signal anddetermining the SNR of the first signal based at least in part upon themeasured SNR of the second signal.
 18. The device of claim 17, whereinsaid first signal is a pilot signal and said second signal is a rateindicator signal; and wherein said rate indicator signal indicates adata rate at which a data signal is received by said receiver over athird channel.
 19. The device of claim 18, wherein said data signal isreceived over the third channel at a higher signal power level than saidrate indicator signal and said pilot signal.
 20. The device of claim 18,wherein said processor determines a first energy-per-chip ratio betweenthe rate indicator and pilot signals based at least in part upon saiddata rate at which said data signal is received over said third channel.21. The device of claim 20, wherein said processor determines the SNR ofthe pilot signal based on the measured SNR of the rate indicator signaland the first energy-per-chip ratio between the rate indicator and pilotsignals.
 22. The device of claim 20, wherein said processor determines asecond energy-per-chip ratio between the data and pilot signals based atleast in part upon said data rate at which said data signal is receivedover the third channel.
 23. The device of claim 22, wherein saidprocessor determines the SNR of the data signal based at least upon themeasured SNR of the rate indicator signal and the first and secondenergy-per-chip ratios.
 24. A mobile terminal, comprising: a transmitterfor transmitting a first signal over a first channel and a second signalover a second channel to a base transceiver site, said second signalbeing transmitted at a higher signal power level than said first signal;and wherein said base transceiver site receives said first and secondsignals, measures a signal-to-noise ratio (SNR) of the second signal,and determines the SNR of the first signal based at least in part uponthe measured SNR of the second signal.
 25. The mobile terminal of claim24, wherein said first signal is a pilot signal and said second signalis a rate indicator signal; and wherein said rate indicator signalindicates a data rate at which a data signal is received by said basetransceiver sire over a third channel.
 26. The mobile terminal of claim25, wherein said data signal is received over the third channel at ahigher signal power level than said rate indicator signal and said pilotsignal.
 27. The mobile terminal of claim 25, wherein said basetransceiver site determines a first energy-per-chip ratio between therate indicator and pilot signals based at least in part upon said datarate at which said data signal is received over said third channel. 28.The mobile terminal of claim 27, wherein said base transceiver sitedetermines the SNR of the pilot signal based on the measured SNR of therate indicator signal and the first energy-per-chip ratio between therate indicator and pilot signals.
 29. The mobile terminal of claim 27,wherein said base transceiver site determines a second energy-per-chipratio between the data and pilot signals based at least in part uponsaid data rate at which said data signal is received over the thirdchannel.
 30. The mobile terminal of claim 29, wherein said basetransceiver site determines the SNR of the data signal based at leastupon the measured SNR of the rate indicator signal and the first andsecond energy-per-chip ratios.
 31. A computer readable media embodying amethod for a wireless communication system, the method comprising:receiving a first signal over a first channel and a second signal over asecond channel, said second signal being received at a higher signalpower level than said first signal; measuring a signal-to-noise ratio(SNR) of the second signal; and determining the SNR of the first signalbased at least in part upon the measured SNR of the second signal. 32.The method of claim 31, wherein said receiving at least a first signalover a first channel and a second signal over a second channel furthercomprises: receiving at least a pilot signal over a first channel and arate indicator signal over a second channel, said rate indicator signalindicating a data rate at which a data signal is received over a thirdchannel.
 33. The method of claim 32, wherein said data signal isreceived over the third channel at a higher signal power level than saidrate indicator signal and said pilot signal.
 34. The method of claim 32,further comprising: determining a first energy-per-chip ratio betweenthe rate indicator and pilot signals based at least in part upon saiddata rate at which said data signal is received over said third channel.35. The method of claim 34, wherein said determining the SNR of thefirst signal further comprises: determining the SNR of the pilot signalbased on the measured SNR of the rate indicator signal and the firstenergy-per-chip ratio between the rate indicator and pilot signals. 36.The method of claim 34, further comprising: determining a secondenergy-per-chip ratio between the data and pilot signals based at leastin part upon said data rate at which said data signal is received overthe third channel.
 37. The method of claim 36, further comprising:determining the SNR of the data signal based at least upon the measuredSNR of the rate indicator signal and the first and secondenergy-per-chip ratios.